1. Field of the Invention
The present invention relates to a method for producing allyl alcohols. Particularly, it relates to a method for producing allyl alcohols, wherein diallyl ethers are heat-treated in the presence of a catalyst containing a palladium compound and a phosphorus compound to convert them to allyl alcohols.
2. Discussion of Background
Alkadienols, especially octadienols including octa-2,7-dien-1-ol, are industrially important compounds, as intermediates for producing n-octanol or its esters.
Heretofore, as a method for producing alkadienols, a method is known in which a conjugated alkadiene and water are subjected to a dimerization reaction in the presence of a catalyst containing a palladium compound and a phosphorus compound and, if necessary, carbon dioxide. For example, Japanese Examined Patent Publication No. 10565/1975 discloses a dimerization reaction employing triphenylphosphine as a ligand of the palladium compound. However, the yield and selectivity for alkadienols are inadequate, and high boiling point substances such as diallyl ethers (e.g. dialkadienyl ethers) are produced as by-products.
Production of such high boiling point substances as by-products consumes the starting material conjugated alkadiene uselessly, whereby the yield of desired allyl alcohols (e.g. alkadienols) will be reduced. Besides, when the catalyst solution is recycled for use, the high boiling by-products tend to accumulate in the recycled catalyst solution and show a chemical inhibitory action against the catalytic activities, or they tend to increase the viscosity of the recycled catalyst solution to substantially hinder the reaction.
Further, Japanese Unexamined Patent Publication No. 88536/1990 discloses a method in which alkadienols are formed from a conjugated alkadiene and water, then from the obtained reaction solution, alkadienols and the solvent are separated to obtain a solution containing dialkadienyl ethers and a palladium compound, and the solution is heat-treated at a temperature of at least 90.degree. C. to decompose dialkadienyl ethers to alkatrienes, etc. However, the method disclosed in this Japanese Unexamined Patent Publication No. 88536/1990 is not a method for recovering useful components by the decomposition of dialkadienyl ethers, as the decomposition products are water and alkatrienes, etc., although it is effective to decompose and remove dialkadienyl ethers as high boiling point by-products. Besides, in the method disclosed in Japanese Unexamined Patent Publication No. 88536/1990, desired alkadienols are also likely to be decomposed to alkatrienes, etc. Accordingly, it has a drawback that alkadienols have to be separated by distillation under an industrially extremely difficult condition such as 1.8 mmHg prior to the heat treatment. Further, in such a case, due to the distillation under a high vacuum condition and the accompanying heat treatment, decomposition products of the treated solution will be distilled. Consequently, the palladium and the phosphorus compound are concentrated and precipitated, whereby an industrial operation will be extremely difficult.
Under these circumstances, it has been desired to develop a method for producing allyl alcohols (such as alkadienols), whereby diallyl ethers (such as dialkadienyl ethers) can be effectively used.